36 Z. Anal. Chem., Band 254, Heft 1 (1971)

Nous avons utflisd ce mode op6ratoire pour le dosage du chrome dans quelques produits sodiques et dans des eaux industriellcs. Les rdsultats obtenus sont en bonne concordance avec ceux fournis par concentra t ion et spectrographie [1]:

Nature du produit Teneurs en chrome en mg/kg du produit tel quel

Spectro- Spectro- graphie photometric

Saumure NaC1 0,015 0,016 0,011 0,014 0,016 0,013 0,013 0,011

Lessive NaOH 0,06 0,05 0,10 0,06 0,07 0,10 0,08 0,08

E a u de pompage 0,010 0,015 0,012 0,013

Bibliographic 1. Farquhar, ~5. C., Hill, J. A., English, M. i~I. : Anal. Chem.

88, 208 (1966); el. Z. Anal. Chem. 281, 75 (1967). 2. Fujinaga, T., Kuwamoto, T., Nakayama, E.: Talanta

16, 1225 (1969). 3 . - - -- -- Satake, M.: Japan Analyst 18, 398 (1969); cf.

Z. Anal. Chem. 251, 309 (1970). 4. -- -- Yonekubo, T., Satake, M. : Japan Analyst 18, 1113

(1969); el. Z. Anal. Chem. 249, 884 (1970). 5. --Satake, M., Yonekubo, T.: Japan Analyst 19, 216

(1970). 6. Gillet, A. G., Jr. : Z. Anal. Chem. 247, 163 (1969). 7. Satake, M.: Talanta 17 (1970) (en pr6paration).

Dr. A. C. Gillet, Jr. Solvay et Cie., Dept. Recherche 310 Rue de Ransbeek, Bruxelles-12, Belgique

UV-Spectrophotometric Determination of 2,4- and 2,6-Dimethoxybenzoic Acid and 4,6-Dimethoxyisophthalic Acid in Presence of Each Other* UV-Spektrophotometrische Bestimmung yon 2,4- sowie 2,6-Dimethoxybenzoes~ure und 4,6-Dimethoxyisophthal- s~ure nebeneinander

J. Rvssv, M. Rvssv and T. SZX~T6 Chem. Pharm. Research Institute, Cluj (Romania)

Received November 4, 1970

I n the ease of the carboxylat ion of resorcinol under conditions different f rom those of the previous s tudy

* Studies on the Carboxylation of Resorcinol. Part IL

the method described earlier [1], gives quite erro- neous results, as besides the 2,6-dihydroxybenzoic acid (I), 2,4-dihydroxybenzoie acid (II) and resor- cinol ( I I I ) there appears in the solution another p roduc t of react ion: 4,6-dihydroxyisophthalic acid (IV).

As our purpose now was to obtain the 2,6-dimeth- oxybenzoic acid (I a) and 2,4-dimethoxybenzoic acid ( I Ia) , the d ihydroxy compounds were no t isolated, the ethers being directly obtained.

The resorcylic ether was separated during the synthesis and consequently did no t interfere with the determination. The 2,6-dimethoxybenzoic acid (Is) , 2,4-dimethoxybenzoic acid (Ha) and 4,6-di- methoxyisophthal ic acid (IVa) have been determined by an U.V.-spectrophotometr ic method, based on absorption measurements as 290, 255, and 230 nm, and on the calculation of the concentrat ions by means of the following equations:

E2s o ~ 166 • CIa -~ 254 • CIIa -t- 1710 • CIva E255 ~ l l0• ~ 745• ~ 546• E290 ~ 87 • CI~ ~ 352 • CHa % 206 • CIva

where E means the absorpt ion values measured and C the concentrat ions of compounds I a , H a and IVa . Though all the components exhibit an absorpt ion in the considered range we obtained sat isfactory results employing 0.I N HC1 solutions, containing 0.2 to 2.0 • 10 -~ Moles/1 of the I I a and IVa components and 0.4--4.0 • 10 -5 Mol/1 of the I a component . Cells of 0 .5--1.0 cm thickness were used.

Some typical results are given in the Table.

Table. Results o] determinations

Mixture I a I I a IV a No. mg-~ mg-~ mg-~

given found given found given found

1 0.800 0.807 0.180 0.171 0.212 0.211 2 0.400 0.415 0.180 0.172 0.212 0.213 3 0.075 0.065 0.370 0.380 0.042 0.051 4 0.400 0.386 0.370 0.360 0.420 0.415 5 0.410 0.410 0.040 0.038 0.410 0.410 6 0.410 0.414 0.040 0.032 0.041 0.050 7 0.205 0.199 0.390 0.380 0.204 0.215 8 0.410 0.412 0.200 0.210 0.410 0.420 9 0.400 0.395 0.410 0.402 0.045 0,055

Re]erence

1. Russu, J., Rnssu, M., Sz~nt6, T.: Z. Anal. Chem. 251, 3O5 (1970).

Jana R u s s u

Chem. Pharm. Research Institute Str. Avram Iancu 1~o. 18, Clu], Romania